An assembly station is fed with parts for connecting to one another by a handling tool (a robot) which “entrusts” the part it is transporting to tooling specific to the assembly station, which tool then ensures that the part is put accurately into place and is clamped firmly in place. That conventional disposition suffers from the major drawback of requiring the assembly station to implement tools that are dedicated to each of the parts received. Consequently, to switch from manufacturing one product to another, although it is possible to retain a single handling robot, it is necessary to change the tooling for positioning and clamping the parts relative to the assembly station. That requirement constitutes a major limit on assembly station flexibility, i.e. on its capacity to receive different types of part. It is necessary to have one set of tools for each part and to fit the station with tool-changing means so that such a changeover can be performed as quickly as possible. The assembly station then becomes very cluttered by means for handling these sets of tools (which are often presented in the form of prefitted pallets. It is also necessary for the handling means to be manufactured with care so that the sets of tools are put into place as accurately as possible within the station and do not give rise to unacceptable dispersion in the accuracy with which the parts for assembling together are put into place. Furthermore, such tool changes still require time and that constitutes a factor for lengthening assembly cycle times, which necessarily leads to increased production costs.
Nowadays, the accuracy of handling robots concerning control over the paths they follow and the coordinates of the starting and ending positions of each such path are becoming entirely compatible with the accuracy required for positioning parts in the frame of reference of an assembly station. As a result, it is possible merely by changing the programming of a handling robot to put various different parts accurately into place in an assembly frame of reference within which, likewise by suitable and varying programming, it is possible to give accurate positions to assembly tools such as welding clamps.
It is thus possible to eliminate the specific positioning tools that were previously necessary in assembly stations. Unfortunately, the structure of a robot is unsuitable for withstanding the forces to which parts are subjected by the action of the assembly tools in order to keep each part firmly in position during an assembly operation (e.g. by welding). This leads to a major risk of the resulting assembly having the wrong shape.